Apparatuses with these characteristics, for example for the checking of a crankpin diameter of a crankshaft rotating with orbital motion about a geometrical axis in the course of the machining in a grinding machine, are disclosed in international patent application published with No. WO-A-9712724, filed by the same applicant of the present application.
In particular, according to the embodiments shown and described in the above mentioned international patent application, the apparatuses have Vee-shaped reference devices that rest on the crankpin to be checked, and maintain correct cooperation with the surface of the crankpin substantially owing to the force of gravity. The embodiments disclosed in the above-mentioned patent application guarantee excellent metrological results and small forces of inertia, and the standards of performance of the apparatuses with these characteristics, manufactured by the applicant of the present patent application, confirm the remarkable quality and reliability of the applications. Furthermore, these known apparatuses can be utilized for carrying out roundness checkings of the cylindrical surfaces of the pins, while the crankshaft is assembled and rotates on the grinding machine.
International patent application published with No. WO-A-0166306, filed by the same applicant of the present patent application, relates to an apparatus and a method for checking the roundness of crankpins in orbital rotation on a grinding machine. This international patent application describes the detecting of diameter dimensions of the crankpin, at predetermined angular positions of the crankshaft rotation, by means of a gauging head including a feeler and Vee-shaped reference surfaces that rest on the piece and a transducer that detects displacements of the feeler along a direction of measurement coincident with the bisecting line of the Vee or slightly inclined with respect to it.
The detected dimensions are processed, for both compensating alterations due to the particular type of head used (modulation of the shape errors of the checked surface that is in contact with the reference Vee) and carrying out other compensations for keeping into account the position taken by the head on the surface of the crankpin, more specifically the angularly arranged position of the point of contact of the feeler with respect to a known reference position, that depends on the relative arrangement between the support element and the crankshaft and on the characteristics and consequent configurations taken by the support device carrying the head. FIGS. 1a and 1b show, in an extremely simplified form, some parts of a known apparatus, coupled to the grinding-wheel slide of a grinding machine, in the course of the checkings of a cylindrical crankpin. In order to emphasize how the angular arrangement of the measurement direction D defined by feeler T depends on the mutual position between piece to be checked and coupling area of the apparatus, FIGS. 1a and 1b show two different checking conditions. In the first condition (FIG. 1a) the apparatus checks the pin while the latter is in contact with the grinding wheel, in the second condition (FIG. 1b), the checking takes place while the grinding-wheel slide is retracted with respect to the piece. It is also necessary to realize that in the course of the checking of a pin in orbital motion (for example a crankpin), variations in the configuration of the support device cause consequent variations in the angular arrangement of the feeler.
The method according to international patent application WO-A-0166306 enables to achieve excellent results, notwithstanding the unavoidable approximations due to the various processings, that are based on the theoretic behavior of the involved mechanic parts.